Injection control in semiconductor power devices

ABSTRACT

Semiconductor power devices can be formed on substrate structure having a lightly doped semiconductor substrate of a first conductivity type or a second conductivity type opposite to the first conductivity type. A semiconductive first buffer layer of the first conductivity type formed above the substrate. A doping concentration of the first buffer layer is greater than a doping concentration of the substrate. A second buffer layer of the second conductivity type formed above the first buffer layer. An epitaxial layer of the second conductivity type formed above the second buffer layer. One or more heavily doped regions of the second conductivity type are formed through portions of the first buffer layer from the second buffer layer and into corresponding portions of the substrate. This abstract is provided with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

CLAIM OF PRIORITY

This application is a continuation of U.S. patent application Ser. No.14/292,692, filed May 30, 2014, the entire contents of which areincorporated herein by reference in their entirety.

FIELD OF THE INVENTION

This present disclosure relates in general to the semiconductor powerdevices, and more particularly to configurations and methods formanufacturing semiconductor power devices to improve thecollector-emitter saturation voltage and avoid backside implant.

BACKGROUND OF THE INVENTIONS

An insulated gate bipolar transistor (IGBT) is a semiconductor powerdevice with a compositing structure that combines features of ametal-oxide-semiconductor field effect transistor (MOSFET) and a bipolarjunction transistor (BJT). With the MOSFET's characteristic of easycontrol with a gate electrode, the bipolar current flow mechanism, andthe advantages of shorter switching time and lower power loss, IGBTshave been widely applied in a high voltage and high power application.

In order to lower the on-resistance of the IGBT, field stop IGBTs havebeen developed. Field stop IGBTs generally have a (n-type) buffer layerat the bottom of the drift region and a thin implanted (p-type)collector region below the buffer layer. The collector region has areduced number of charges compared to punch through IGBTs, and so hascontrolled minority carrier injection. The buffer layer acts as a fieldstop and terminates the electric field. For field stop IGBTs, it isimportant to carefully control the charge levels in the buffer layer andthe collector layer.

Conventional technologies to configure and manufacture semiconductorpower devices, particularly field stop IGBT devices, are stillconfronted with difficulties and limitations due to various tradeoffsand uncertainties in controlling the thickness and dopant concentrationof the backside layers. In IGBT devices, there is a tradeoff betweenconduction loss and turn-off switching losses, E_(off). Conduction lossdepends upon the collector to emitter saturation voltage V_(ce(SAT)) atrated current. Greater carrier injection while the device is on improvesthe conductivity of the device, thus reducing conduction loss. Increasedcarrier injection would, however, cause higher turn-off switching lossesbecause of energy dissipated in clearing out injected carriers duringturn-off. However, for applications where switching losses do notdominate, greater carrier injection from the backside can reduceconduction loss and improve the collector to emitter saturation voltageV_(ce(SAT)) at rated current. Examples of applications where switchinglosses do not dominate include, e.g., induction heating, and lowfrequency motor drives.

There are several conventional methods of manufacturing IGBTs withbackside processing steps. In one implementation, the starting materialis a single semiconductor substrate layer (such as N type) without anadditional epitaxial layer atop. The top side processing steps areperformed to form the IGBT structures on the top side of the substrate.After backside grinding, a backside N-type implant is performed to forman N-type buffer layer followed by a P-type implant to form the bottom Pcollector layer. A backside metal layer is formed to function as thedrain/collector electrode. This process requires two backside implantoperations and backside activation/anneal operation. In addition, theanneal processes on the backside layer can only be performed at a lowtemperature due to the limitations imposed by the already existingtopside IGBT structures and metal layer. The laser anneal mitigates thisby using short pulses of localized high temperatures on the waferbackside, which do not increase the wafer topside temperaturesubstantially. However, laser anneal are typically shallow (typically onthe order of 1 μm), and cannot anneal out the damages cause by thedeeper N implant that is used to create the N buffer region.

An alternative implementation includes a starting material of an N-typesubstrate supporting an N-type epitaxial layer over it. The substrate isdoped with volumetric doping concentration of the N-type buffer layer.After the topside processing steps to form IGBT structures on the topside of the substrate, the backside grinding is performed to reduce thelower N-type substrate layer to a predefined thickness. Ideally, thepre-defined thickness together with the volumetric doping concentrationof the lower N-substrate layer result in the desired per area chargelevel of the buffer region. A bottom P-type layer is then formed from abackside P-type implant. A backside metal layer is in turn formed tofunction as the drain electrode. This implementation does not require ahigh temperature anneal after backside grinding for the N-type bufferlayer because it is already doped as the starting lower substrate layer.However, these manufacturing processes encounter difficulties beingunable to accurately control the backside grinding thickness with atightly controlled tolerance. Variations in the thicknesses of N-typebuffer layer vary charge levels in the N-type buffer layer and thusadversely affecting performance of the IGBT devices.

Another class of IGBT called the Reverse Conducting IGBT (RC-IGBT) arepopular in the industry. These IGBTs combine the free-wheeling diode inthe device structure, thereby eliminating the need for co-packaging aseparate Diode chip with the IGBT. However, the conventional method formaking RC-IGBT relies on a masking step on the wafer backside of a verythin wafer, after it has completed the topside process and has beenbackground to 2 to 4 mil thickness. At such thicknesses, the siliconwafers are warped & difficult to handle which makes the process ofmasking extremely difficult.

It is within this context that embodiments of the present inventionarise.

BRIEF DESCRIPTION OF THE DRAWINGS

Objects and advantages of the invention will become apparent uponreading the following detailed description and upon reference to theaccompanying drawings in which:

FIG. 1 is a cross-sectional schematic diagram of a semiconductor powerdevice according to an embodiment of the present disclosure.

FIGS. 2A-2D are a sequence of cross-sectional schematic diagramsillustrating a method of fabrication of the device of FIG. 1.

FIG. 3 is a cross-sectional schematic diagram of a semiconductor powerdevice according to an embodiment of the present disclosure.

FIGS. 4A-4F are a sequence of cross-sectional schematic diagramsillustrating a method of fabrication of the device of FIG. 3.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

In the following Detailed Description, reference is made to theaccompanying drawings, which form a part hereof, and in which is shownby way of illustration specific embodiments in which the invention maybe practiced. In this regard, directional terminology, such as “top,”“bottom,” “front,” “back,” “leading,” “trailing,” “above”, “below”, “ontop of”, “underneath”, etc., is used with reference to the orientationof the figure(s) being described. Because components of embodiments ofthe present invention can be positioned in a number of differentorientations, the directional terminology is used for purposes ofillustration and is in no way limiting. It is to be understood thatother embodiments may be utilized and structural or logical changes maybe made without departing from the scope of the present invention. Thefollowing detailed description, therefore, is not to be taken in alimiting sense, and the scope of the present invention is defined by theappended claims.

Commonly owned U.S. Pat. No. 8,283,213 proposes a configuration andmethod for manufacturing a semiconductor power device with a bufferregion formed as part of the starting wafer with its thickness andcharge level already set before topside processing, entire contents ofwhich are herein incorporated by reference. Specifically, the processesstart with forming a light doped layer of either P-type or N-typesemiconductor materials. An epitaxial growth process is performed toform at least a buffer layer and a drift layer over the substrate. Afterthe topside processing steps to form IGBT structures on the top side ofthe substrate, the backside grinding is performed to reduce thesubstrate to a thickness about 100 to 120 microns. A backside implant isperformed to form the bottom collector layer. The backside implant isfollowed by low temperature or rapid thermal anneal. Thereafter, abackside metal layer is formed to function as the drain/collectorelectrode. Such configuration and manufacturing processes limit theamount of activation by rapid thermal anneal at about 450° C. for about60 seconds or anneal process at 350° C. for about 6 hours. The annealprocess has to be handled carefully because the top metal layer may meltat 400° C. Nevertheless, amount of activation is less than 0.1%. Whilethis amount of activation may be sufficient for applications whereswitching losses dominate, it is not enough for applications whereconduction losses dominate.

Some other proposed methods involve using laser annealing from thebackside to get local melting and re-crystallization of silicon. Whilethese methods may improve the amount of activation up to 100%, it cannotbe applied for annealing the damages that are deeper in silicon, in therange of 2.5 μm and above, since laser penetration in silicon is in theorder of 1 μm.

The present disclosure describes an improved configuration and methodfor manufacturing a semiconductor power device that has high levelactivation with deep implant and improved V_(cesat) for applicationwhere conduction loss tends to dominate. Specifically, for an N-typedevice as an example, an additional P-type layer is formed on either alightly doped P-type or N-type substrate. With the P-type layer, theamount of injection, the doping and thickness of the P layer can becontrolled. Activation of 100% can be achieved during high temperaturetopside processing. The annealing process is required only for makingthe ohmic contact to the backside metal.

Aspects of the present disclosure describe a substrate structure for asemiconductor device. The substrate structure includes a lightly dopedsemiconductor substrate of a first conductivity type or a secondconductivity type opposite to the first conductivity type. Asemiconductive first buffer layer of the first conductivity type isformed above the lightly doped semiconductor substrate. A dopingconcentration of the first buffer layer is greater than a dopingconcentration of the lightly doped semiconductor substrate. Asemiconductive second buffer layer of the second conductivity type isformed above the first buffer layer. A semiconductive epitaxial layer ofthe second conductivity type formed above the second buffer layer,wherein a doping concentration of the epitaxial layer is greater than adoping concentration of the second buffer layer.

In some aspects one or more semiconductor power device structures formedat a top side of the substrate structure.

In some implementations, the one or more power device structures mayinclude one or more trenches formed in the epitaxial layer, wherein aconductive material is disposed in the trenches with a dielectricmaterial lining the trenches between the conductive material andsidewalls of the trenches; one or more planar gates each formed over acorresponding trench with an insulation layer provided between theplanar gate and the corresponding trench; and one or more heavily dopedcontact regions of the second conductivity each surrounded by acorresponding body region of the first conductivity type, wherein thebody region of the first conductivity type is formed in the substratestructure and between two neighboring trenches.

Other aspects of the present disclosure describe a method forfabricating a substrate and epitaxial structure. The method comprisesforming a substrate structure comprising a lightly doped semiconductorsubstrate of a first conductivity type or a second conductivity typeopposite to the first conductivity type; forming a semiconductive firstbuffer layer of the first conductivity type above the lightly dopedsemiconductor substrate, wherein a doping concentration of the firstbuffer layer is greater than a doping concentration of the lightly dopedsemiconductor substrate; forming a semiconductive second buffer layer ofthe second conductivity type above the first buffer layer; and forming asemiconductive epitaxial layer of the second conductivity type above thesecond buffer layer, wherein a doping concentration of the epitaxiallayer is greater than a doping concentration of the second buffer layer.

Aspects of the present disclosure will be described below in terms ofexamples and it is to be understood that such disclosure is not to beinterpreted as limiting. Various alterations and modifications will nodoubt become apparent to those skilled in the art after reading thedisclosure.

FIG. 1 illustrates a semiconductor power device according to an aspectof the present disclosure. In the following description, N-type devicesare described for purposes of illustration. It should be noted that thepresent disclosure may be applied to P-type devices by reversing thepolarities of the conductivity types of the various regions and layers.In the example shown in FIG. 1, the device is an insulated gate bipolartransistor (IGBT) device. However, the configurations and methodsdescribed in the present disclosure are not limited to IGBT devices butalso other semiconductor power devices, such as thyristors,MOS-controlled thyristors or reverse conducting IGBT devices.

As shown in FIG. 1, a plurality of N-type IGBT devices 100 include theIGBT structures formed on top of a starting material that may include asubstrate 102-1 supporting a P-type layer 104, an N-type buffer layer106, an N-type drift layer 108 and an N-type injection enhancement layer109. Each of the IGBT structures may include a conductive material 112filled in a trench 113 formed from a top surface of the N-type injectionenhancement layer 109 into a top portion of the N-type epitaxial layer108. The trench 113 is lined with a dielectric material 115 between theconductive material 112 and sidewalls of the trench 113. The IGBTstructure also has a planar gate 118 supported on top of a gateinsulation layer 117 (e.g., gate oxide). The planar gate can be drawnparallel or orthogonal to the direction of the trenches. In addition, anN-type source region 116 is encompassed by a P-type body region 114formed in a top portion of the N-type injection enhancement layer 109between adjacent trenches 113. The P-type body region 114 is extendedbelow and from the sides of the N-type source region 116 to a regionunderneath the gate insulation layer 117 and is spaced away fromsidewalls of the trenches 113 as shown in FIG. 1. A top metal layer 120is disposed on a top surface of the IGBT structures. Furthermore, asecond P-type layer 132 and a backside metal layer 134 are attached tothe backside of the substrate 102-1.

FIGS. 2A-2D are a sequence of cross-sectional views for illustrating theprocesses for manufacturing a semiconductor device of FIG. 1. FIG. 2Ashows a lightly doped substrate 102 of an N-type, P-type or intrinsicsemiconductor material. By way of example and not by way of limitation,the doping concentration of an N-type/P-type substrate 102 may be in arange between 1e13 to 1e15 cm⁻³ (or less than 1e¹⁵ cm⁻³).

FIG. 2B shows that a P-type layer 104, an N-type layer 106, an N-typeepitaxial layer 108 and an N-type injection enhancement layer 109 areformed above the substrate 102. In one implementation, the process mayinclude a 4-step epitaxial growth process to form these layers on top ofeach other as shown in FIG. 2B. Specifically, a first layer of theepitaxially grown layer is the P-type layer 104. By way of example, andnot by way of limitation, the P-type layer 104 may have a dopingconcentration between approximately 1e15 cm⁻³ and 1e18 cm⁻³, higher thanthat of the substrate 102. The P-type layer 104 may be in a thicknessabout 2-5 μm. Next, an N-type layer 106 may be epitaxially grown abovethe P-type layer 104. By way of example and not by way of limitation,the N-type layer 106 may have a doping concentration betweenapproximately 1e15 cm⁻³ and 1e17 cm⁻³, also higher than the substrate102. The N-type layer 106 may be in a thickness range of about of about3 μm to about 15 μm thick. In addition, an N-type epitaxial layer 108may be grown above the N-type layer 106. By way of example and not byway of limitation, the N-type epitaxial layer 108 may be lightly dopedwith a concentration between approximately 1e12 cm⁻³ and 1e15 cm⁻³. TheN epitaxial layer 108 may be in a thickness range of about 30 μm toabout 150 μm thick. Finally, the N injection enhancement layer 109 maybe epitaxially grown on top of the N epitaxial layer 108. By way ofexample and not by way of limitation, the N injection enhancement layer109 may have a doping concentration between approximately 1e15 cm⁻³ and5e17 cm⁻³, higher than that of the substrate 102. The N injectionenhancement layer 109 may be in a thickness range of about 2 μm to about5 μm thick. By way of example, and not by way of limitation, the N-typedopants may be phosphorus, arsenic, or antimony, and the P-type dopantsmay be boron or BF₂.

In another implementation, the process may include a blanket implant ofP-type dopants to form the P-type layer 104, followed by a 3-stepepitaxial growth to form the N-type layer 106, the N-type epitaxiallayer 108 and an N-type injection enhancement layer 109. In thisimplementation, the depth and doping concentration of the P-type layer104 can be controlled by the implant energy and the implant dose. By wayof example and not by way of limitation, the P-type layer 104 may beformed by ion implantation at an energy of about 200K eV to about 1000KeV with a dose of about 1e12 to about 1e14 cm⁻². The dopants used toform the P-type layer 104 may be boron or BF₂. Dopants of the P-typelayer 104 would be fully activated by the thermal cycles from thetopside processing as discussed below.

After the starting material has been formed, a conventional topsideprocessing can be performed to form the topside IGBT structures as shownin FIG. 2C. Specifically, trenches 113 are formed by etching through theN-type injection enhancement layer 109 and into the N-type epitaxiallayer 108. The trenches 113 may be lined with a dielectric material 115(e.g., oxide). In one implementation, the dielectric material 115 may beformed on the sidewalls of the trenches through an oxide depositionprocess. Thereafter, a conductive material (e.g., polysilicon) is thenfilled into the trenches 113 to form trench gate 112. A planar gate 118is formed over the trenches 113 with an insulation layer 117therebetween. A P-type body region 114 and the N-type source region 116are formed (e.g., by implantation) in the N-type injection enhancementlayer 109. By way of example and not by way of limitation, the P-typebody region 114 may have a doping concentration between approximately5e16 cm⁻³ and 5e17 cm⁻³. Also the N-type source region 116 may beheavily doped with a doping concentration between 1e18 cm⁻³ and 1e20cm⁻³. A top metal layer 120 is formed on the top surface contacting theN-type source region 116 and P-type body region 114.

Additional processing may be performed to produce the finished devices100, as shown in FIG. 2D. For example, after the topside processing iscompleted, a backside grinding can be carried out to grind the back ofthe substrate 102 down to a remaining substrate 102-1 with a pre-definedthickness. By way of example, the thickness of the substrate 102-1 maybe between about 1 μm and about 10 μm. It should be noted that thethickness of the remaining substrate 102-1 is not critical so long asthe back grinding process does not reach all the way to the P-type layer104. A second P-type layer 132 may then be formed at the bottom surfaceof the substrate 102-1 by backside implant and a low temperature annealto partially activate the dopant Thereafter, a backside metal layer 134can be formed on the bottom surface as the drain electrode followed by apost metal anneal for alloying & forming an ohmic contact.

According to the embodiment above, the N-type layer 106 is alreadyformed together with its dopants in crystalline form through epitaxialgrowth before the topside processing is carried out to form the topmetal layers of the IGBT device. Depending on the implementation method,the P-type layer 104 may be either activated when it is epitaxiallygrown, or by the thermal cycles from the topside processing. Thus, alater annealing process is not necessary to activate the P-type orN-type layer dopants because the dopants are already activated.

FIG. 3 illustrates an implementation of a reverse conducting IGBT deviceaccording to an aspect of the present disclosure. Generally, a reverseconducting IGBT device requires an N-type buffer region or an N-typedrift region to be selectively shorted to the collector electrode. Thisshort allows the formation of an anti-parallel diode, which enablescurrent conduction in the IGBT in a reverse mode (i.e., current flowsfrom a cathode/emitter terminal to the anode/collector terminal). Thus,a heavily doped N-type region is usually embedded in an anode/collectorregion of the IGBT. It should be noted that N-type devices are describedfor purposes of illustration. The present disclosure may be applied toP-type IGBT devices by reversing the polarities of the regions andlayers. In addition, in the following description, elements in FIGS. 3and 4A-4F identical to the elements discussed in connection with FIGS. 1and 2A-2D will be identified using the same last two digital referencenumeral. For simplicity, the description of these identical elementswill not be repeated below and reference will be made to the abovedescription in connection with FIGS. 1 and 2A-2D.

FIG. 3 depicts a plurality of N-type reverse conducting IGBT devices 300that is substantially similar to IGBT devices 100 of FIG. 1 with theexception that the starting material of the reverse conducting IGBTdevices 300 includes a heavily doped N-type region 350 for each reverseconducting IGBT device. The N-type region 350 extends through the P-typelayer 304 and the substrate 302-1 and a second P layer 332. The N-typeregion 350 is in contact with the N-type layer 306 at one end and thebackside metal layer 334 at the other end.

The IGBT structures including a trench gate 312, a planar gate 318, anN-type source region 314, a P-type body region 316 are formed in thestarting material, and a top metal layer 320 is disposed on a topsurface of the IGBT structures as shown in FIG. 3. Furthermore, a secondP-type layer 332 and a backside metal layer 334 are formed at thebackside of the substrate 302-1. The second P-type layer 332 provides anohmic contact between the substrate 302-1 and the metal layer 334.

FIGS. 4A-4F are a sequence of cross-sectional views for illustrating theprocesses for manufacturing a semiconductor device of FIG. 3. FIG. 4Ashows a lightly doped substrate 302 of an N-type, P-type or intrinsicsemiconductor material. In one example, the doping concentration of anN-type/P-type substrate 302 may be in a range between 1e12 to 1e15 cm⁻³(or less than 1e¹⁵ cm⁻³). In one implementation, the process starts withforming a P-type layer 304 in the substrate 302 by epitaxial growthprocess. By way of example, and not by way of limitation, the P-typelayer 304 may have a doping concentration between approximately 1e15cm⁻³ and 1e18 cm⁻³, higher than that of the substrate 302. The P bufferlayer 304 may be in a thickness about 2 to 5 μm. Next, a masked implantmay be performed to form a heavily doped N-type region 350 in thesubstrate 302 as shown in FIG. 4C. By way of example and not by way oflimitation, the N-type region 350 may be formed by ion implantation atabout 100k eV to about 1000K eV with a dose of about 5e14 to about 1e16cm⁻². In another implementation, the process starts with forming aP-type layer 304 in the substrate 302 by a blanket implant of P-typedopants. In this implementation, the depth and doping concentration ofthe P-type layer 304 can be controlled by the implant energy and theimplant dose. By way of example and not by way of limitation, the P-typelayer 304 may be formed by ion implantation at about 200K eV to about1000K eV with a dose of about 1e12 to about 1e14 cm⁻². Next, a maskedimplant may be performed to form an N-type region 350 in the substrate302 as shown in FIG. 4C. In this implementation, the N-type region 350may be formed prior to forming the implanted P-type layer 304.

After forming the P-type layer 304 and the N-type region 350, a 3-stepepitaxial growth is performed to form an N-type layer 306, the N-typeepitaxial layer 308, and the N-type injection enhancement layer 309, asshown in FIG. 4D. Subsequent processing forms the topside IGBTstructures, as shown in FIG. 4E. Additional processing may be performedto produce the finished devices 300, as shown in FIG. 4F. For example,after the topside processing, a back grinding is carried out to grindthe back of the substrate 302 down to a remaining substrate 302-1. Asecond P-type layer 332 is formed at the bottom surface of the substrate102-1 by backside implant and a low temperature anneal to partiallyactivate the dopant Then a backside metal layer 334 is formed on thebottom surface as the drain electrode. The backside grinding isperformed such that the N-type layer 306 is electrically connected tocreate RC effect.

Table I below shows performance comparison of various semiconductorpower devices. Device 1 is a conventional device without a P-type layerformed on the top side of the substrate. Device 2 has an epitaxiallygrown P-type layer having a resistivity of 0.9 ohm-cm and a thickness of5 μm. For Device 3, 500 keV Boron with a dose of 5e¹² cm⁻² is implantedinto the substrate to form a P-type layer. For Device 4, its P-typelayer is implanted at 500 keV with a dose of 7.5e¹² cm⁻². From thetable, devices according to the present disclosure (e.g., Devices 2-4)have lower V_(ce(SAT)) and thus improved performance for applicationswhere induction heating switching losses do not dominate.

TABLE I Thickness of P layer the N buffer V_(ce(SAT)) BV_turn Device 1N/A 5 1.51 1650 Device 2 Epitaxial grown, 11 1.39 1639 0.9 ohm · cm, 5μm Device 3 Implant with 500 11 1.421 1673 Kev and 5.00E+12 Device 4Implant with 500 11 1.37 1652 Kev and 7.50E+12

While the above is a complete description of the preferred embodimentsof the present invention, it is possible to use various alternatives,modifications, and equivalents. Therefore, the scope of the presentinvention should be determined not with reference to the abovedescription but should, instead, be determined with reference to theappended claims, along with their full scope of equivalents. Anyfeature, whether preferred or not, may be combined with any otherfeature, whether preferred or not. In the claims that follow, theindefinite article “A” or “An” refers to a quantity of one or more ofthe item following the article, except where expressly stated otherwise.The appended claims are not to be interpreted as includingmeans-plus-function limitations, unless such a limitation is explicitlyrecited in a given claim using the phrase “means for”. Any element in aclaim that does not explicitly state “means for” or “step for”performing a specified function, is not to be interpreted as a “means”or “step” clause as specified in 35 USC §112(f).

What is claimed is:
 1. A substrate structure, comprising: a lightlydoped semiconductor substrate of a first conductivity type or a secondconductivity type opposite to the first conductivity type; asemiconductive first buffer layer of the first conductivity type formedabove the lightly doped semiconductor substrate, wherein a dopingconcentration of the first buffer layer is greater than a dopingconcentration of the lightly doped semiconductor substrate; asemiconductive second buffer layer of the second conductivity typeformed above the first buffer layer; a semiconductive epitaxial layer ofthe second conductivity type formed above the second buffer layer; andone or more heavily doped regions of the second conductivity type formedthrough portions of the first buffer layer from the second buffer layerand into corresponding portions of the lightly doped semiconductorsubstrate.
 2. The substrate structure of claim 1, wherein the firstconductivity type is P-type and the second conductivity type is N-type.3. The substrate structure of claim 1, further comprising an injectionenhancement layer of the second conductivity type formed above theepitaxial layer, wherein a doping concentration of the injectionenhancement layer is greater than the doping concentration of theepitaxial layer of the second conductivity type.
 4. The substratestructure of claim 1, further comprising a semiconductor layer of thefirst conductivity type formed on a backside of the lightly dopedsemiconductor substrate.
 5. The substrate structure of claim 4, whereinthe one or more heavily doped regions of the second conductivity typeare formed through the lightly doped semiconductor substrate and throughthe semiconductor layer of the first conductivity type formed on thebackside of the lightly doped semiconductor substrate.
 6. The substratestructure of claim 5, further comprising a metal layer formed on asurface of the semiconductor layer of the first conductivity type formedon the backside of the lightly doped semiconductor substrate, whereinthe one or more heavily doped regions of the second conductivity typemake electrical contact with the metal layer.
 7. A semiconductor powerdevice, comprising: a substrate structure comprising a lightly dopedsemiconductor substrate of a first conductivity type or a secondconductivity type opposite to the first conductivity type; asemiconductive first buffer layer of the first conductivity type formedabove the lightly doped semiconductor substrate, wherein a dopingconcentration of the first buffer layer is greater than a dopingconcentration of the lightly doped semiconductor substrate; asemiconductive second buffer layer of the second conductivity typeformed above the first buffer layer; and a semiconductive epitaxiallayer of the second conductivity type formed above the second bufferlayer; one or more heavily doped regions of the second conductivity typeformed through portions of the first buffer layer from the second bufferlayer and into corresponding portions of the lightly doped semiconductorsubstrate; and one or more semiconductor power device structures formedat a top side of the substrate structure.
 8. The device of claim 7,wherein the one or more semiconductor power device structures includeone or more trenches formed in the substrate structure, wherein aconductive material is disposed in the trenches with a dielectricmaterial lining the trenches between the conductive material andsidewalls of the trenches.
 9. The device of claim 8, wherein the one ormore semiconductor power device structures further include one or moreplanar gates each formed over a corresponding trench with an insulationlayer provided between each planar gate and corresponding trench. 10.The device of claim 9, wherein the one or more semiconductor powerdevice structures further include one or more heavily doped contactregions of the second conductivity type, each contact region beingsurrounded by a corresponding body region of the first conductivitytype, wherein the body region is formed in the substrate structurebetween two neighboring trenches.
 11. The device of claim 7, wherein theone or more semiconductor power device structures includes one or moreinsulated gate bipolar transistor (IGBT) devices thyristors,MOS-controlled thyristors, or reverse conducting IGBT devices.
 12. Thedevice of claim 7, wherein the first conductivity type is P-type and thesecond conductivity type is N-type.
 13. The device of claim 7, furthercomprising an injection enhancement layer of the second conductivitytype formed above the epitaxial layer, wherein a doping concentration ofthe injection enhancement layer is greater than the doping concentrationof the epitaxial layer of the second conductivity type.
 14. The deviceof claim 7, further comprising a semiconductor layer of the firstconductivity type formed on a backside of the lightly dopedsemiconductor substrate.
 15. The device of claim 14, wherein the one ormore heavily doped regions of the second conductivity type are formedthrough the lightly doped semiconductor substrate and through thesemiconductor layer of the first conductivity type formed on thebackside of the lightly doped semiconductor substrate.
 16. The device ofclaim 15, further comprising a metal layer formed on a surface of thesemiconductor layer of the first conductivity type formed on thebackside of the lightly doped semiconductor substrate, wherein the oneor more heavily doped regions of the second conductivity type makeelectrical contact with the metal layer.
 17. A method, comprising:forming a substrate structure comprising a lightly doped semiconductorsubstrate of a first conductivity type or a second conductivity typeopposite to the first conductivity type; forming a semiconductive firstbuffer layer of the first conductivity type above the lightly dopedsemiconductor substrate, wherein a doping concentration of the firstbuffer layer is greater than a doping concentration of the lightly dopedsemiconductor substrate; forming a semiconductive second buffer layer ofthe second conductivity type above the first buffer layer; forming asemiconductive epitaxial layer of the second conductivity type above thesecond buffer layer; and forming one or more heavily doped regions ofthe second conductivity type through portions of the first buffer layerfrom the second buffer layer and into corresponding portions of thelightly doped semiconductor substrate.
 18. The method of claim 17,wherein the first conductivity type is P-type and the secondconductivity type is N-type.
 19. The method of claim 17, furthercomprising forming an injection enhancement layer of the secondconductivity type above the epitaxial layer, wherein a dopingconcentration of the injection enhancement layer is greater than thedoping concentration of the epitaxial layer.
 20. The method of claim 17,wherein forming a layer of a first conductivity type comprisesepitaxially growing the layer of the first conductivity type.
 21. Themethod of claim 17, wherein forming the first buffer layer comprisesblanket implant of first conductivity type dopants in the lightly dopedsemiconductor substrate.
 22. The method of claim 17, wherein forming theone or more heavily doped substrate regions of the second conductivitytype comprises masked implant of second conductivity dopants intoportions of the layer of the first conductivity and lightly dopedsemiconductor substrate.
 23. The method of claim 17, further comprisingforming one or more semiconductor power device structures at a top sideof the substrate structure.
 24. The method of claim 23, wherein formingthe one or more semiconductor power device structures includes formingone or more trenches in the substrate structure, disposing a conductivematerial in the trenches with a dielectric material lining the trenchesbetween the conductive material and sidewalls of the trenches.
 25. Themethod of claim 24, wherein forming the one or more semiconductor powerdevice structures further includes forming one or more planar gates eachover a corresponding trench and providing an insulation layer betweeneach planar gate and corresponding trench.
 26. The method of claim 25,wherein forming the one or more semiconductor power device structuresfurther includes forming one or more heavily doped contact regions ofthe second conductivity type, wherein each contact region is surroundedby a corresponding body region of the first conductivity type, whereinthe body region is formed in the substrate structure between twoneighboring trenches.
 27. The method of claim 20, wherein the one ormore semiconductor power device structures includes one or moreinsulated gate bipolar transistor (IGBT) devices thyristors,MOS-controlled thyristors, or reverse conducting IGBT devices.
 28. Themethod of claim 17, further comprising forming a semiconductor layer ofthe first conductivity type on a backside of the lightly dopedsemiconductor substrate.
 29. The method of claim 28, wherein the one ormore heavily doped regions of the second conductivity type are formedthrough the lightly doped semiconductor substrate and through thesemiconductor layer of the first conductivity type formed on thebackside of the lightly doped semiconductor substrate.
 30. The method ofclaim 29, further comprising forming a metal layer on a surface of thesemiconductor layer of the first conductivity type formed on thebackside of the lightly doped semiconductor substrate, wherein the oneor more heavily doped regions of the second conductivity type makeelectrical contact with the metal layer.